GridView not Rebinding Properly After Postback

I have a GridView that has a DataSourceID pointing to an ObjectDataSource. The ObjectDataSource points to a method that returns a LINQ IQueryable by using the TypeName, SelectMethod, and SelectCountMethod properties of the ObjectDataSource control. What happens is that the data loads properly upfront. However, on postback, if I remove the rows from the GridView and try to rebind using the explicit GridView.DataBind(), it doesn't work. I know LINQ is returning the proper rowcount and such because I've called the countmethod and it returns the proper rowcount. Here's a quick example:

<asp:GridView ID="TestGridView" runat="server" PageSize="20" 
    AutoGenerateColumns="false" AllowPaging="true" 
    AllowSorting="false" DataSourceID="TestDataSource">
    <Columns>
        ...
    </Columns>
</asp:GridView>

<asp:ObjectDataSource ID="TestDataSource" runat="server" 
    EnablePaging="true" SelectCountMethod="GetDetailCount" 
    SelectMethod="GetDetails" TypeName="MyApp.PageClass" />

I've tried adding a button and adding the TestGridView.DataBind(); method to that. I've tried adding it to the Page_PreRender event. No matter what I try, it's not working.

As someone suggested below, I've tried moving it to Page_Load as well, and no go. Here's a rough example of my code:

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        // Set "initial" query parameters, then ...
        BindData();
    }
}

private void BindData()
{
    // EDITED: Removed the code below since I'm not looking to delete the
    //         rows from the database, but rather get the GridView to rebind
    //         which its not.
    ////Remove all current rows from the GridView
    //int colCount = TestGridView.Rows.Count;
    //for (int x = 1; x <= colCount; x++)
    //{
    //    TestGridView.DeleteRow(x);
    //}

    // Bind GridView to the ObjectDataSource
    TestGridView.DataBind();
}

protected void RegenerateImageButton_Click(object sender, ImageClickEventArgs e)
{
    // Set "updated" query parameters, then ...
    BindData();
}

After looking at the code behind a bit more, I stumbled across page property values being stored in ViewState. Once I changed it over to Session, they work.